SS4.02 The Role of Microbiology in Trace Metal and Organic Contaminant Cycling in Aquatic Systems
Date: Wednesday, June 12, 2002
Time: 10:15:00 AM
Location: Esquimalt
 
Marvin-DiPasqualeMC, U.S. Geological Survey, Menlo Park, CA, USA, mmarvin@usgs.gov
Agee, J, L, U.S. Geological Survey, Menlo Park, CA, USA, jlagee@usgs.gov
Kieu, L, H, U.S. Geological Survey, Menlo Park, CA, USA, lhkieu@usgs.gov
Jaffe, B, E, U.S. Geological Survey, Santa Cruz, CA, USA, bjaffe@usgs.gov
 
MERCURY METHYLATION AND DEMETHYLATION IN NORTH SAN FRANCISCO BAY WETLANDS: THE RHIZOSPHERE INFLUENCE
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The San Francisco Bay (SFB) estuary is contaminated with mercury as a result of the historic mining of this element in the nearby coastal mountains, and its use in gold/silver mining in the Sierra-Nevada region to the east during the mid-to-late 1800s. We examined microbial methylmercury (MeHg) production and degradation dynamics in northern SFB sediments from vegetated salt marshes, non-vegetated salt-marsh sloughs, and estuarine open waters (non-vegetated). MeHg concentrations and net production rates were highest in pickleweed and tule dominated marsh and in non-vegetated marsh slough sediments. All three open water (2 m depth) sites and one highly oxidized (> +300 mV), under-saturated, mixed-vegetation site exhibited comparatively low MeHg concentrations and production rates. We propose a conceptual model in which increased MeHg production is associated with the plant root zone (rhizosphere) in saturated salt marsh sediment, as a result of enhanced oxygen and biodegradable DOC transfer from the plants to the sediment. The transferred oxygen reoxidizes reduced sulfur compounds to sulfate, which stimulates MeHg-producing sulfate-reducing bacteria. This model may partially explain previous reports of the wetlands as zones of enhanced MeHg production.